The season 2018-2019 of the Champions League is about to start. 8 pools with each 4 teams compete for the big Cup. Each team has about 21 to 25 players, and in total 784 players are involved.
In sports it is well known that there is a so-called Relative Age Effect (RAE). This implies that children born earlier in the year can be better in school but in particular in sports. Evidence of the RAE is reported for NHL hockey (1) and Football (2).
Just out of curiosity: Would the RAE also hold for the players in the about to begin Champions League? Based on the birth days data (3), the following graph can be drawn (where 1 is January, and 12 is December)
88 players are born in January, 90 in February, whereas in November and December only 52 and 47 celebrate their birthdays, respectively. The downward trend as the year proceeds is clearly visible.
So, also in a competition involving players from all kinds of countries, age levels, and positions in the field, the RAE prominently holds.
(1) Deaner, R.O, A. Lowen and S. Cobley (2013), Born at the wrong time: Selection bias in the NHL draft, PLOS One, 8 (2), e57753, and the many citations therein.
(2) Doyle, J.R. and P.A. Bottomley (2018), Relative age effect in elite soccer: More early-born players, but no better valued, and no paragon clubs or countries, PLOS One, February 8 2018.
(3) Based on data available from Voetbal International (September 12, 2018), pages 34-67.